Extensive efforts have been devoted to research and develop an antenna that can be used throughout the world, covering all the current cellular bands and complying with all communication standards, plus having the convenient surface mount technique for low cost and high reliability.
Cellular and mobile devices are now operating with quad-band antennas, these bands are the 850 (GSM), 900 (EGSM), 1800 (DCS) and 1900 MHz (PCS), but with the introduction of 3G and 4G technologies for higher speed and data transfer rate in cellular applications, three new bands are introduced in the radiofrequency spectrum, 700 (LTE), 1700 (UMTS) and the 2100 MHz (WCDMA), but not exclusive to these communication standards.
With the introduction of the new 700 MHz (LTE) band in North America, it is indeed higher complexity for its integration while keeping the antenna size similar to quad-band antenna, satisfying the current demands for small devices. Over the years is observed how the devices tend to be smaller, but with the new low frequency band presents a real challenge in miniaturization and the bandwidth must be increased to incorporate more new frequencies: 1710 and 2100 MHz bands. New technologies, materials, topologies, form factors and novel designs must be studied to continue miniaturizing the antennas and complains with the demands of the current and future market's needs.
The Basic formula for antenna design dictates that the length of the antenna is one-quarter of the wavelength at the desired frequency, 35 mm (one quarter of the wavelength in free space) is the physical length for a pure straight cable or, monopole antenna at 2100 MHz, contrasting with 108 mm of physical length for a basic monopole antenna at 700 MHz. Reducing the antenna at low frequencies present a real challenge, but some techniques are studied like increasing the dielectric constant of the material that enclose the antenna, bending the metallic radiated element and find the specific geometrical shape that reduce the space occupied by the antenna. The ratio of miniaturizing and antenna via higher dielectric constant is equal to 1/√∈, where ∈ is the dielectric constant of the material used as a carrier for the metallic path of the antenna.
The flexible material Kapton used on this antenna has a dielectric constant of 3.8. The total thickness of the flexible material is approximately 0.85 mm, enclosing the radiated elements. Using this flexible material for the antenna design presents propitious conditions to achieve two important phenomenons in the antenna design. The first one is enclosing the radiated elements with this Kapton material, reducing the size of the antenna even with a thin factor, due the currents of the electromagnetic fields are traveling in the surface of the radiated elements having an interaction with the high dielectric constant material, and at the same time the second condition, having the thin material with high dielectric constant supporting the radiated elements, is almost imperceptible in compare with the air that surrounds the antenna; this means the antenna is surrounded mainly by air, as a consequence resulting with an effective dielectric constant (computation the two materials with different dielectric constant) very close to the free-space.
Presenting the advantages of a complete surface mount technology integration, for an easy, cheap, time saving, and automated integration, eliminating the necessity of human interactions for soldering purposes, pogo pin and spring contacts. All of this assembling and integration qualities ends in delivering a reliable and consistence antenna performance, reflected on better signal reception, making the antenna feasibly for telematic, tracking, telemedicine, automotive, fleet management, vehicle diagnostics, remote monitoring and also in the emerging telemedical diagnostic market.